What Is Polyoxymethylene?
Polyoxymethylene (POM) is a resin with acetal bonds in the main chain and is mainly a homopolymer of oxymethylene or a copolymer of oxymethylene and oxyethylene. It has advantages such as excellent rigidity, abrasion resistance, and chemical resistance, and is used for pump parts, gears, bearings, and fasteners.
On the other hand, Polyoxymethylene has disadvantages such as white color and poor transparency, poor weather resistance due to the cleavage of carbon-oxygen bonds in the main chain by UV light, and low resistance to strong acids due to hydrolysis.
Advantages and Uses of Polyoxymethylene
Polyoxymethylene (POM) is a resin with an acetal bond in the main chain, mainly consisting of oxymethylene repeating units. Polyoxymethylene is called POM for polyoxymethylene, but some POMs also contain oxyethylene.
Polyoxymethylene has advantages in rigidity, abrasion resistance, chemical resistance, low water absorption, and low coefficient of friction with metals. Because of these advantages, Polyoxymethylene is used in a wide range of industries and applications, including pump parts, water pipe joints, gears and bearings, fasteners, and laundry tubs.
Structure of Polyoxymethylene
Polyoxymethylene is obtained through anionic polymerization of formaldehyde. After polymerization, the ends have an unstable hemiacetal structure, which is stabilized by acetylation with acetic anhydride. Copolymer POM, which is polymerized by adding oxyethylene in addition to formaldehyde, is also commercially available.
Compared to copolymers, formaldehyde homopolymers have higher crystallinity and mechanical strength, but lower moldability and thermal stability. Copolymers also have better long-term mechanical properties than homopolymers, making them suitable for use in mechanical parts.
Disadvantages of Polyoxymethylene
While Polyoxymethylene is a plastic with excellent properties, it also has some disadvantages: POM is white, lacks transparency, and has low weather resistance because the carbon-oxygen bonds or acetylated ends of the main chain are cleaved by UV light. POM with improved durability has been commercialized by adding colorants such as carbon black.
POM also has no durability against strong acids because the carbon-oxygen bonds in its main chain undergo hydrolysis when it comes into contact with acids. Other disadvantages include poor adhesion due to the lack of adhesives compatible with POM.